Dc current interruption system able to open a dc line with inductive behaviour

ABSTRACT

The invention pertains to a DC current interruption system able to open a DC line with inductive behaviour, comprising a primary mechanical breaker (S 0 ), a secondary mechanical breaker (S 1 ) and an electronic overvoltage protection circuit (B 1,  B 2 ) comprising at least one transistor. The DC current interruption system of the invention furthermore comprises an electronic opening system ( 72, 76 ) comprising a passive circuit able to auto-bias the electronic protection circuit (B 1,  B 2 ) upon the opening of said primary mechanical breaker (S 0 ), so as to trigger a switching of said at least one transistor (M 1,  M 2,  IG 1 ) making it possible to limit the voltage and the current in the DC line, total interruption of said DC line being obtained by subsequent opening of said secondary mechanical breaker (S 1 ).

The invention relates to a DC current interruption system able to open aDC line with inductive behaviour.

More generally, the field of the invention is the field of DC breakers.

DC breakers are widely used in various industrial, aeronautic andautomobile applications or for energy distribution. They make itpossible to obtain a full charge on a long distance DC line or bus,which therefore has an inductive behaviour, in order to insulate asource of energy from a network or a charge.

It is known that at high power, the opening of a DC line generatesstrong electric arcs caused by the energy stored in the electricitynetwork. In order to interrupt these electric arcs, various solutionsbased on expensive and complex mechanical breakers are known in priorart.

Hybrid solutions implementing both an electronic portion withsemiconductor base and a mechanical portion have been proposed.

The article “Micro-Arcing and Arc Erosion Minimization Using a DC HybridSwitching Device” by J. Swingler and J. McBride, published in thejournal IEEE Transactions on Components and Packaging Technologies, vol.31, no. 2, published on 2 Jun. 2008, presents a hybrid breakercomprising a series of three mechanical breakers and a field effecttransistor of the MOSFET type of which the function is to prevent theelectric arc effect. For proper operation, the actuation of themechanical breakers in this solution must be carried out according to aprecise sequence which is an operating constraint. In addition, thissolution is suited only for voltages around 40Volts (V) and 2.5 Amperes(A), and therefore is not suited for applications with DC lines at ahigher voltage.

Many applications, as for example photovoltaic applications, requirevoltages around 600V, and currents around 30A.

It is desirable to overcome the disadvantages of prior art, and obtain aDC mechanical breaker that is simplified and that can be used inparticular in a high voltage domain.

To this end, the invention has for purpose a DC current interruptionsystem able to open a DC line with inductive behaviour, comprising aprimary mechanical breaker, a secondary mechanical breaker and anelectronic overvoltage protection circuit comprising at least onetransistor. The DC current interruption system is characterised in thatit further comprises an electronic opening system comprising a passivecircuit able to auto-bias the electronic protection circuit upon theopening of said primary mechanical breaker, so as to trigger a switchingof said at least one transistor making it possible to limit the voltageand the current in the DC line, with total interruption of said DC linebeing obtained by subsequent opening of said secondary mechanicalbreaker.

Advantageously, the electronic opening system takes over from theprimary mechanical breaker and allows for the delayed self-biasing ofthe protection circuit which is able to absorb the energy released bythe transient of the source, which makes it possible to carry out aninterruption while still preventing any electric arc. The protectioncircuit makes it possible to substantially limit the current intensity,and consequently the actuation of the secondary mechanical breaker doesnot need to be synchronised with the actuation of the primary mechanicalbreaker, therefore there is no strong constraint in sequencing breakers.In the current interruption system according to the invention, simpleand low-cost mechanical breakers are sufficient.

The DC current interruption system according to the invention can haveone or several of the characteristics hereinbelow:

-   -   the electronic protection circuit comprises a plurality of field        effect transistors mounted in parallel, able to switch to an        ohmic mode in a first step after opening of said primary        breaker, then to a breakdown mode in a second step when the        voltage reaches a predetermined value;    -   the electronic protection circuit further comprises a breakdown        balancing system, making it possible to operate said plurality        of field effect transistors in breakdown mode        quasi-simultaneously;    -   the breakdown balancing system comprises a resistor mounted in        series with each field effect transistor;    -   the electronic protection circuit comprises a first block able        to limit the voltage comprising at least one transistor of the        first type, and a second block able to limit the current        comprising at least one transistor of the second type;    -   the second block comprises, for each transistor of the second        type, a resistor mounted in series with said transistor;    -   the DC current interruption system comprises two electronic        opening systems, i.e. a first electronic opening system with        fast self-biasing able to actuate said first block and a second        electronic opening system with slow self-biasing able to actuate        said second block, in such a way as to allow for, upon the        opening of said primary mechanical breaker, a limitation of the        voltage by said first block followed by a current limitation by        said second block;    -   upon the opening of said primary breaker (S0), the following        phases are sequenced:    -   implementation of said first block by the electronic opening        system with fast self-biasing, said at least one transistor of        the first type operating in ohmic mode,    -   implementation of said second block by the electronic opening        system with slow self-biasing, said at least one transistor of        the first type being in non-passing mode,    -   implementation of said first block when the voltage reaches a        predetermined value, said at least one transistor of the first        type operating in breakdown mode;    -   said transistor of the first type is a MOSFET transistor and        said transistor of the second type is an IGBT transistor;    -   a said electronic opening system comprises at least one passive        circuit comprised of a diode mounted in series with a capacitor,        and a resistor mounted in parallel with said capacitor, and    -   a number of transistors mounted in parallel in said protection        circuit are determined according to the constraints in voltage,        current and inductance of said DC line.

Other characteristics and advantages of the invention will appear in thedescription provided hereinbelow, for the purposes of information and isin no way limited, in reference to the annexed figures, among which:

FIG. 1 is a block diagram of a DC current interruption system;

FIG. 2 is a diagram showing a first embodiment of a DC currentinterruption system according to the invention;

FIGS. 3 to 6 show the operation of the DC current interruption system ofFIG. 2;

FIG. 7 is a diagram showing a second embodiment of a DC currentinterruption system according to the invention;

FIG. 8 is a diagram showing a third embodiment of a DC currentinterruption system according to the invention;

FIG. 9 is a diagram showing a fourth embodiment of a DC currentinterruption system according to the invention,

FIG. 10 is a graph comprising curves that show the change in the currentand voltage upon the actuation of the DC current interruption systemaccording to the fourth embodiment for a 20V/2.5A line, and

FIG. 11 is a diagram showing a fifth embodiment of a DC currentinterruption system according to the invention.

A DC current interruption system with field effect transistors of theMOSFET type (“Metal Oxide Semiconductor Field Effect Transistor”) isdescribed in what follows. However, the invention is applied with anytype of semiconductor component, and in particular with any type offield effect transistor.

The favoured application considered here is the use of the DC currentinterruption system of the invention in the framework of the productionof photovoltaic current, generating a bus current or a 600V/30A highvoltage DC line. The invention however applies more generally with alarge range of DC bus constraints, in a voltage range ranging from 20Vto 900V (currently the maximum voltage for a component of the MOSFET),with the calibre in current being linked to the number of semiconductorcomponents placed in parallel. The various components are dimensioned inrelation to the target application, according to the constraints of theDC bus.

The DC current interruption system 10, referred hereinafter simply asinterruption system, shown in FIG. 1, is able to open a DC line 12between a source S and a charge C. This system comprises two mechanicalbreakers S0, S1, as well as an electronic opening system with a passivecircuit 14 which plays the role of an electronic breaker with a delayfor an overvoltage protection circuit B, which is a block comprising atleast one semiconductor component or transistor.

When the primary breaker S0 is actuated, the current passes into theelectronic opening system 14, which actuates via self-biasing theswitching of the transistor or transistors of the protection circuit Bwhich quickly reach their saturation regime, which triggers theiropening and makes it possible to prevent any electric arc.

In addition, the protection circuit B limits the current to a value thatis practically zero, which then allows the opening of the secondarybreaker S1 for a total interruption.

Thanks to the electronic opening system 14 no external control device ofthe electronic protection circuit is required and the electric arc isavoided.

FIG. 2 shows a first embodiment of a DC current interruption system 20with transistors of the MOSFET type. In the example of the figure theelectronic opening system 14 comprises a passive circuit 22 comprised ofa diode D1 mounted in series with a capacitor C2, and a resistor R4mounted in parallel to the capacitor C2. A resistor R3 is mounted inseries with the passive circuit 22.

The electronic opening system 14 shown in FIG. 2 further comprises aresistor R5.

The interruption system 20 further comprises a Zener ZD2 diode mountedin parallel to the resistor R5. This diode is optional and has foreffect to protect the gate of the transistor against a temporaryovervoltage which could cause its destruction.

The electronic protection circuit B comprises two MOSFET components M1and M2 mounted in parallel, and resistors R1, R2 each mounted in serieswith one of the transistors.

The resistors form a balancing system 24 for sharing the energy betweenthe two MOSFET components M1 and M2 in breakdown mode. Indeed, inpractice, the breakdown voltage Vbr of a MOSFET component can beslightly different from the theoretical manufactured breakdown voltage.Even a slight difference between the breakdown voltages of MOSFETcomponents mounted in parallel can have a substantial impact on thedistribution of the energy. Indeed, if for example the MOSFET M1 has abreakdown voltage that is higher than the MOSFET M2, the MOSFET M2 firstswitches to breakdown mode and absorbs all of the energy of the circuit,and no current passes through the MOSFET M1 at a higher breakdownvoltage. In this case, there is no distribution of energy between thetwo MOSFET components, although the very objective of mounting severalsuch components in parallel is to allow for the absorption of energythat is higher than that which can be supported by a single component.

In order to prevent the imbalance which can occur if the MOSFETcomponents mounted in parallel do not have equal breakdown voltages inpractice, resistors of a low value are placed on the drain side of eachMOSFET component. For example resistors R1=R2=1 Ohms for respectivecomponents M1 and M2 having a theoretical breakdown voltage of Vbr32900V and respective practical breakdown voltages of plus or minus 10Varound the breakdown voltage are recommended.

As such, when the MOSFET component of which the breakdown voltage is thelowest enters into breakdown mode, its drain current increasessignificantly, and the voltage at the terminals of the correspondingbalancing resistor is also largely increased. This voltage also appliesfor the parallel branch, which makes it possible to reach the breakdownvoltage also in the second branch, and makes it possible to actuate thesecond MOSFET component in breakdown mode also.

The interruption system 20 having a passive capacitive circuit 22 and aplurality of MOSFET transistors mounted in parallel is adapted in orderto limit the voltage and the current for a DC line with low constraints,having an inductance less than 3 mH (milli Henrys) and a current rangingup to 10A.

FIGS. 3 to 6 show in detail the operation of the interruption system 20of FIG. 2.

In nominal operation, such as is shown in FIG. 3, the two breakers S0and S1 are closed, the components M1 and M2 are in blocked mode. The DCbus is closed, and the current is flowing according to the line 30 shownin FIG. 3.

When the primary breaker S0 is open as shown in FIG. 4, and thesecondary breaker S1 is maintained closed, the current is flowingaccording to the line 32 during the charge of the capacitive passivecircuit, and the respective gates of the MOSFET components M1 and M2 arequickly charged via R3 according to the flow 34 and 36 (shown as dottedlines in FIG. 4 e). The two transistors are passing in ohmic mode; thecurrent is flowing according to the lines 38, 40 of FIG. 4 while thecapacitive passive circuit continues to be charged. The choice of thevalues of R3, R5 and of C2 makes it possible to control this chargingphase. For example R3=3 Ohms, R5=10 Ohms and C2=10 nF (nano Farads) areselected for a current of 5A. When the charge of the capacitor C2 iscompleted, the latter acts as an open breaker, as shown in FIG. 5. Thegates of the MOSFET components discharge via R5 causing an increase inthe voltage Vds for each MOSFET, then the MOSFET components switch tobreakdown mode, shown as dotted lines 42 and 44 in FIG. 5. The diode D1has for effect to prevent substantial oscillations of the voltage Vdsafter the breakdown event.

After the breakdown event of the two MOSFET transistors, a low residualcurrent continues to flow, as shown in FIG. 6, according to the line 46through the resistors R6-R3-R5. The secondary breaker S1 is then open inorder to interrupt this low residual current. The opening of S1finalises the opening of the DC bus 12 and completely isolates thecharge of the source.

In practice, the number of MOSFET components to be placed in parallel inthe protection circuit B depends on the specific breakdown voltage ofthe components and of the constraints, in particular for voltage andinductance, of the DC bus.

As such, for a 600V/30A bus, nine MOSFET components with CoolMOS(Registered Trademark) technology of the SPA17N80C3 type are used havinga breakdown voltage of 800V for a bus with inductance of 3 mH, orfourteen such components for a bus with inductance of 5 mH. The numberof MOSFET components required is therefore rather high for a highvoltage bus.

FIG. 7 shows a second embodiment of a DC current interruption systemaccording to the invention, which is better suited for a high voltage DCbus as it requires a lesser number of MOSFET components in parallel.

In this embodiment, the interruption system combines transistors of theMOSFET type and an IGBT transistor (“Insulated Gate BipolarTransistor”).

The interruption system 70 comprises a first electronic opening system72 with passive circuit 74, which is a self-biasing system with fastopening, able to actuate a first block B1 comprising two transistors ofthe first type, MOSFET transistors M1 and M2, mounted in parallel, and asecond electronic opening system 76 with passive circuit 78, which is aself-biasing system with slow opening able to actuate a second block B2,comprised of one or several transistors of the second type, here a IGBTIG1 transistor. The blocks B1 and B2 form a circuit that is functionallyequivalent to the protection circuit B.

Each of the passive circuits 74, 78 is comprised of a diode (D2, D1)mounted in series with a capacitor (C3 C2), a resistor (R6, R4) alsobeing mounted in parallel with the capacitor, in a manner similar to thepassive circuit 22 of FIG. 2.

The opening delay for forming a fast opening system, of which thecapacitor is charged faster than that of the slow opening system, iscontrolled by the choice of the time constant for the control branch,for example 100 ns for the fastest, and 1.5 μs for the slowest, with thetime constant obtained by a choice of suitable values for capacitanceand resistance.

For example, C2=10 nF, R6=800 kOhms can be selected for the passivecircuit 76, and C2=1 nF, R4=800 kOhms for the passive circuit 78. Thediodes D1, D2 are selected to pass all of the current of the DC line ina very short time. For example, 1 kV, 30A diodes are used.

Each electronic opening system 72, 76 further comprises resistors R3, R5for the opening system 76, R7, 68 for the opening system 72, in a mannersimilar to the opening system 14 of FIG. 2. For example, the numericalvalues of these resistors take the following values: R3=50 Ohms, R5=1500Ohms, R7=1 Ohms, R8=10 Ohms.

The first block B1 comprising MOSFET components is intended to limit thevoltage and to prevent electric arcs, and the second block B2 allows fora limitation of faster current.

The first block B1 further comprises a balancing system 79 withresistors mounted in series at the drain of each transistor MOSFET, in amanner similar to the balancing system 24 of FIG. 2, and having the samefunction.

In operation, upon the opening of the primary breaker SO, the passivecircuit 74 is charged and the gates of the MOSFET transistors of theblock B1 are quickly charged. The MOSFET components start to operate inohmic mode. During this time, the second passive circuit 78 is alsocharged, and the IGBT component of the second block B2 becomes passing.

The passive circuit 74 having reached its full charge, an interruptionoccurs, and the MOSFET M1 and M2 are also interrupted.

The IGBT component of the second block B2 takes over until the capacitorC2 of the passive circuit 78 is fully charged. Then, the IGBT componentswitches and substantially limits the current of the DC bus.

This substantial decrease in the current causes an overvoltage peak,which is absorbed by the MOSFET components which switch to breakdownmode when the voltage of the DC bus exceeds their breakdown voltage Vbr.As explained hereinabove in reference to FIG. 2, the balancing system 79makes it possible to distribute the energy absorption between thevarious MOSFET transistors.

The operation in breakdown mode of the transistors makes is possible toprevent an operation in overvoltage of the IGBT component, and thereforeto preserve this component.

After the breakdown event, the MOSFET transistors of the block B1 aswell as the IGBT transistor of the block B2 are in interrupted mode, thecurrent is reduced to a low residual current, which can easily beinterrupted by the secondary breaker S1.

In a third embodiment shown in FIG. 8, the second block B2 of theinterruption system 80 is formed of several IGBT mounted in parallel.Indeed, the interruption capacity of a single IGBT component, describedin the SOA (“safe operating area”) associated with the component, whichspecifies for how long a given electric power pulse can be applied tothe IGBT, can be insufficient to absorb the transient current of thecurrent bus.

The number of IGBT components to be inserted into the second block B2depends on the constraints of the DC bus, and also on the breakdownvoltages of the MOSFET transistors of the first block B1. In thisembodiment, the voltage withstand of the IGBT components must be higherthan the voltage Vbr of the MOSFET components. The voltage withstand ofthe MOSFET and their maximum breakdown energy must make it possible todissipate the energy stored in the network.

As such, for example, one or several IGBT 1 KV 50A can be takenassociated with one or several MOSFET 900V 0.7 mJ (milli-Joules), inorder to obtain a fast interruption.

FIG. 9 shows a fourth embodiment of an interruption system according tothe invention, which is optimised in the number of components and incost.

The interruption system 90 of FIG. 9 is similar to the interruptionsystem 70 of FIG. 7, and comprises the primary S0 and secondary S1breakers, fast 72 and slow 76 electronic opening systems, the blocks B1and B2.

Contrary to the embodiment of FIG. 7, the block B2 further comprises aresistor R9 mounted in series with the collector of the IGBT component,in such a way as to assist with the switching of this component. Indeed,a portion of the energy in the conduction phase of the IGBT will bedissipated by the component R9, which makes it possible to reduce theconstraints on the IGBT component and to replace the IGBT in aguaranteed operating mode.

The choice of the value for the resistor R9 is carried out according tothe characteristics of the IGBT component. For example, a resistor R9=40Ohms is chosen with a 25 A/1200 V IGBT component.

In practice, by using an interruption system 90 with resistanceassistance in the switching of the IGBT components, two 1200V IGBTcomponents (for example FGA20S120M components) can be used and twoMOSFET components with breakdown voltage of 900V, for exampleIPP90R340C3 components. This topology makes it possible to reduce thecost of the interruption system in relation to the first embodiment,which would require six MOSFET components with breakdown voltage 900Vmounted in parallel.

The interruption system 90 of FIG. 9 operated in a manner analogous tothe interruption system 70 of which the operation has already beendescribed in reference to FIG. 7.

The opening systems 72, 76 trigger the respective blocks B1 and B2, withfirstly the transistors of B1 in ohmic mode, then the switching of thetransistor or transistors IGBT of the block B2, finally the resuming ofthe block B1 with the MOSFET transistors in breakdown mode in order tofinally reach a current close to zero.

The graph of FIG. 10 shows the change in the current of the bus shown bythe curve 92, and of the voltage at the terminals of the primary breakershown by the curve 94, according to time, when the interruption systemof FIG. 9 is implemented. The curves were plotted using a 20V/2.5 Ademonstrator, but the behaviour is similar for higher voltages.

The graph is divided into five phases, numbered P1 to P5.

In the first phase P1, upon the opening of the primary breaker S0 and ofthe charge of the electronic opening systems 72, 76, during a shortperiod of time, the current and the voltage are at their nominal values.

Then, thanks to the electronic opening system with a fast passivecircuit 72, the block B1 comprising MOSFET transistors switches toconduction in ohmic mode, the current decreases, the voltage increasesduring phase P2. The MOSFET transistors act in order to avoid theelectric arc, while also slightly reducing the current.

The block B2 with IGBT components takes over in the following phase P3in order to continue the limitation of the current, while the block B1switches to non-conductive mode or blocked mode. The voltage continuesto increase until it reaches the value of the breakdown voltage of theMOSFET components. At this moment, the MOSFET transistors of the blockB1 switch to breakdown mode during the phase P4. The voltage remainsstable during the breakdown, the direct current decreases.

Finally, the current reaches a low stable value during the phase P5. Thevoltage curve 94 shows a few oscillations before stabilising. Thesecondary breaker S1 can be actuated at any time in order to totallyinterrupt the current.

FIG. 11 shows a fifth embodiment of an interruption system 100 accordingto the invention, which makes it possible to further improve theprotection against the appearance of electric arcs at the terminals ofthe mechanical contacts in relation to the embodiment of FIG. 9.

In this embodiment, the fast electronic opening system 72 is improved byadding a second branch comprising another passive circuit comprised of adiode D3 mounted in series with a capacitor or capacitance C4, aresistor R10 also mounted in parallel with the capacitor C4. By way ofexample, the values of the following components are recommended forcurrents greater than 3A, the system operating with MOSFET componentswith breakdown voltage Vbr=900V: C4=500 nF, R10=800 kOhms. A diode D3 1kV, 30A is adapted to pass all of the current of the DC line during thetime for putting the MOSFET components in conduction.

The adding of capacitance makes it possible to absorb a portion of theenergy of the network at the first instants after the opening of themechanical breaker S0, which makes it possible to prevent theinitialisation of an electric arc during the time for putting the MOSFETcomponents of the block B1 in conduction. The diode D3 and the resistorR10 control the discharge of the capacitor C4. This system makes itpossible to better prevent the risk of an arc with a low extra cost inrelation to the fourth embodiment, in particular for currents greaterthan 3A.

As such, the various modes of carrying out a DC current lineinterruption system presented allow for the use of low-cost mechanicalbreakers and without substantial constraints on the sequencing of theirrespective openings, and semiconductor electronic components in order toprevent the electric arcs and the overvoltage due to the inductivebehaviour of the DC line. The choice between the topology of theinterruption system comprising solely transistors mounted in parallel orthe topology using two blocks, a block of transistors of the first type,for example MOSFETs, and a block of transistors of the second type, forexample IGBT, is according to the constraints of the DC bus.

1. DC current interruption system adapted to open a DC line withinductive behaviour, comprising a primary mechanical breaker, asecondary mechanical breaker and an electronic overvoltage protectioncircuit comprising at least one transistor, further comprises anelectronic opening system comprising a passive circuit adapted toauto-bias the electronic protection circuit upon the opening of saidprimary mechanical breaker, so as to trigger a switching of said atleast one transistor making it possible to limit the voltage and thecurrent in the DC line, with a total interruption of said DC line beingobtained by subsequent opening of said secondary mechanical breaker. 2.DC current interruption system according to claim 1, wherein saidelectronic protection circuit comprises a plurality of field effecttransistors mounted in parallel, adapted to switch to an ohmic mode in afirst step after opening of said primary breaker, then to a breakdownmode in a second step when the voltage reaches a predetermined value. 3.DC current interruption system according to claim 2, wherein saidelectronic protection circuit further comprises a breakdown balancingsystem, making it possible to operate in breakdown modequasi-simultaneously said plurality of field effect transistors.
 4. DCcurrent interruption system according to claim 3, wherein the breakdownbalancing system comprises a resistor mounted in series with each fieldeffect transistor.
 5. DC current interruption system according to claim1, wherein said electronic protection circuit comprises a first blockadapted to limit the voltage comprising at least one transistor of thefirst type, and a second block adapted to limit the current comprisingat least one transistor of the second type.
 6. DC current interruptionsystem according to claim 5, wherein said second block comprises, foreach transistor of the second type, a resistor mounted in series withsaid transistor.
 7. DC current interruption system according to claim 5,comprising two electronic opening systems, i.e. a first electronicopening systems with fast self-biasing adapted to actuate said firstblock and a second electronic opening system with slow self-biasing ableadapted to actuate said second block, in such a way as to allow, uponthe opening of said primary mechanical breaker, a limitation of thevoltage by said first block followed by a limitation of current by saidsecond block.
 8. DC current interruption system according to claim 5,wherein, upon the opening of said primary breaker, the following phasesare sequenced: implementation of said first block by the electronicopening system with fast self-biasing, said at least one transistor ofthe first type operating in ohmic mode, implementation of said secondblock by the electronic opening system with slow self-biasing, said atleast one transistor of the first type being in non-passing mode,implementation of said first block when the voltage reaches apredetermined value, said at least one transistor of the first typeoperating in breakdown mode.
 9. DC current interruption system accordingto claim 5, wherein said transistor of the first type is a MOSFETtransistor and said transistor of the second type is a IGBT transistor.10. DC current interruption system as claimed in claim 1, wherein saidelectronic opening system comprises at least one passive circuitcomprised of a diode mounted in series with a capacitor, and a resistormounted in parallel with said capacitor.
 11. DC current interruptionsystem as claimed in claim 1, wherein a number of transistors mounted inparallel in said protection circuit is determined according toconstraints in voltage, current and inductance of said DC line.